This invention relates to problems of clock generation in portable dual mode receiver circuits. The invention has particular application to cellular telephone technology where a single compact battery powered receiver must be able to operate on at least two disparate frequency bands. In particular, the invention relates to problems associated with generation of clock signals for digital cellular telephones operative in the AMP/PCS/GSM/EDGE bands (850 MHz, 900 MHz, 1900 MHz bands) which have 200 kHz channel spacing and in the IS136 band (.about.850 MHz band) which has 30 kHz channel spacing.
There is a need to minimize redundant components to save power and space in critical applications such as miniature portable cellular receiver circuit devices. The challenge is to provide a clock into the digital system which can divide down into both 200 kHz and 30 kHz to support the disparate channel spacing requirements. The clock must do so with an integer divider.
Current clock circuits known to the art generate a 13 MHz system clock. This clock frequency is incompatible with 30 kHz channel spacing, since it cannot be divided to 30 kHz by an integer.
What is therefore needed is a clock circuit which provides a compatible signal for all modes of operation.